The present invention is directed to an orthodontic bracket, and in particular, a convertible buccal tube.
A convertible buccal tube is an appliance used by orthodontists during an early phase of treatment to correct malpositioned teeth. The tube is essentially an orthodontic bracket in which the buccal or cheek-facing side of the usual archwire slot is closed by a plate to form a tubular opening of typically rectangular cross section. The plate can be brazed or spot-welded in place. Alternatively, the bracket body can have an integrally formed cover plate with lines of weakness formed by elongated frangible webs extending along the length of the archwire slot, as disclosed in U.S. Pat. No. 4,927,362. In this way, the plate can be removed to convert the buccal tube to a conventional bracket during later stages of treatment.
Convertible buccal tubes have been in use for many years, and reference is made to U.S. Pat. No. 3,391,461 for further background information. Tubes of this type are normally used on younger children whose second molars have not yet grown in, but who have erupted first molars which serve as anchor teeth for an orthodontic archwire. The covered archwire slot provides a terminal buccal-tube anchorage for the archwire during early treatment.
When the second molars erupt, these newly emerged teeth are provided with banded brackets which take over the xe2x80x9canchorxe2x80x9d function and receive the terminal ends of a longer archwire. Prior to installation of the longer archwire, the archwire cover plate on each first-molar tube is removed to convert the tube to a conventional molar bracket, and thus to enable normal edgewise treatment of the first molars.
In known convertible buccal tubes of two-piece construction (bracket and cover plate), production expense is increased by the necessary welding, brazing or other attachment process for securing the plate to the appliance body. These known units also sometimes present cover plate removal problems in that the plate may be awkward and difficult to sever from the underlying body.
In the known design of U.S. Pat. No. 4,927,362, production is complicated by the requirement for an extremely precise frangible web thickness. If the web is too thin, it can fracture prematurely; if too thick, it can be difficult to remove the cover. And if the two separate webs are of different thicknesses, the plate might only shear along one of the webs; thereafter, the orthodontist would have to use an awkward back-and-forth twisting motion in an arc perpendicular to the remaining connected web to achieve fatigue and eventual fracture the web.
It would be desirable to have a convertible buccal tube design which is easy to manufacture. It would be desirable to have a convertible buccal tube design in which the cover plate is integrally formed with the bracket body. It would be desirable to have a convertible buccal tube design in which the areas of weakness provided for the removal of the cover could be easily and reproducibly manufactured. It would be desirable to have a convertible buccal tube design in which the cover plate has an essentially rectangular shape with little or no variation in thickness.
The convertible buccal tube of this invention is an integrally molded, cast, sintered or machined product comprising an orthodontic bracket with a body defining an archwire slot which is covered on the buccal side by an integral cap or plate. The occlusal and gingival sides of the plate are joined to the bracket by integral portions of perforated material forming potential fracture lines which break away when the plate is removed. Preferably the thickness of the cover plate is substantially uniform, with the exceptions of the perforations which have no thickness.
One embodiment of the present invention is directed to a convertible buccal tube having a base designed for direct or indirect attachment of a tooth, a body extending from the base and defining an elongated first archwire slot, and a cover plate extending across and closing a buccal side of said first archwire slot, such plate being integrally joined to the body adjacent opposite sides of the slot by perforated longitudinal connections forming two lines of weakness, whereby the plate can be removed from the body along body of the perforated lines of weakness to open the slot. The perforated longitudinal connections forming two lines of weakness preferably comprise metal alternating with holes formed in the metal. The metal is preferably substantially of the same thickness as the cover plate and the perforations are preferably oblong slots extending through the cover plate. The oblong slots are preferably from about 10-12 mm by about 25-40 mm and the thickness of the cover plate is from about 3-5 mm up to 15-20 mm, even more preferably between about 12.5-15 mm. In other embodiments, a second archwire slot is provided parallel to a first archwire slot, such second archwire slot preferably covered by a plate which is not designed to be removed. The present invention can further comprise an auxiliary tube, preferably positioned parallel to and offset from a first archwire slot.